This study was to establish the floristic composition of northern region in Gyeonggi-province area(126° 45' - 127° 37' E, 37° 31' - 38° 17' N). This work was investigated from April, 1998 to October, 2004. The flora of vascular plants of northern region in Gyeonggi-province were consisted of total 2,030 taxa; 145 families, 656 genera, 1,611 species, 7 subspecies, 320 varieties, 1 subvarieties and 91 formae. Among them, Korea endemic species were composed of 46 families, 85 genera, 84 species, 35 varieties, 1 subvarieties, and 18 formae, total 138 taxa. The rare and endangered plants based on floral region indicated by Ministry of Environment were 416 taxa; Ⅴ rank species 18 taxa, Ⅳ rank species 79 taxa, Ⅲ rank species 111 taxa, Ⅱ rank species 80 taxa, Ⅰ rank species 128 taxa. Also the naturalized plants were 114 species, correspond to 39.7% of among total 287 species appeared in South Korea. The result of PCA, Gwangju mountain chain at northern region of Gyeonggi-province has rich and diverse vascular plants, and there are many Korean endemic, rare and endangered plants. Therefore, Gwangju mountain chain must be the core axis in for conserving the plant biodiversity and richness.